This invention relates to an RF communication system utilizing one or more same frequency repeaters (SFR's) to simultaneously rebroadcast a signal received from a base station thereby extending the area in which the signal can be received by mobile or portable units. More specifically, this invention seeks to minimize the problem of simulcast distortion in such a system. Simulcast distortion refers to interference caused by the reception of first and second signals having approximately equal amplitudes and carrying the same information where the first signal is delayed in time by 100 microseconds or longer relative to the second signal.
An SFR includes a receiver for receiving a signal at a given frequency and a transmitter for retransmitting the signal at the same frequency. Due to the inherent time delays in receiving, processing, and retransmitting a signal, the retransmitted signal broadcast from the SFR is delayed in time relative to the received signal in the order of 100 microseconds or more. Thus, the possibility exists for a mobile unit to experience simulcast distortion as a result of receiving a signal directly from the base station and another signal from an SFR which consists of the base station signal delayed in time.
The problem of simulcast distortion is further complicated when two or more SFR's are utilized to simultaneously retransmit a signal received from a base station. The additional complexity arises because a certain SFR may receive the time delayed signal transmitted by another SFR in addition to the signal from the base station.
The certain SFR will rebroadcast both received signals if they are received at approximately the same signal strength. Thus, a mobile unit which receives the signals retransmitted by the certain SFR may experience simulcast distortion due to the time or phase difference between these retransmitted signals.
It is a general object of this invention to minimize the simulcast distortion problems mentioned above.